FIG. 7 illustrates a configuration block diagram of a conventional battery device. As illustrated in FIG. 7, the conventional battery device schematically includes n batteries BT1 to BTn connected in series, a battery state monitoring circuit 100, a switch circuit 110, a first external terminal 120, and a second external terminal 130.
The batteries BT1 to BTn are, for example, lithium-ion cells, both ends (positive terminal and negative terminal) of each battery is connected to the battery state monitoring circuit 100, the positive terminal of the battery BT1 is connected to one terminal of the switch circuit 110, and the negative terminal of the battery BTn is connected to the second external terminal 130. The battery state monitoring circuit 100 detects the voltages of the respective batteries BT1 to BTn by a voltage detector circuit (not shown) disposed therein to monitor charged/discharged states of the respective batteries BT1 to BTn, and controls an on/off operation of the switch circuit 110 according to the charged/discharged state. The switch circuit 110 switches between connection and disconnection of two terminals thereof under the control of the battery state monitoring circuit 100, one terminal of the switch circuit 110 is connected to the positive terminal of the battery BT1, and another terminal of the switch circuit 110 is connected to the first external terminal 120.
Now, the operation of the above-mentioned conventional battery device is described.
The battery state monitoring circuit 100 controls the switch circuit 110 to be turned on when the voltages of the respective batteries BT1 to BTn are lower than an overcharge voltage and equal to or higher than an overdischarge voltage, thereby connecting the positive terminal of the battery BT1 to the first external terminal 120 to allow charging and discharging of the respective batteries BT1 to BTn. Here, the overcharge voltage indicates a chargeable upper limit voltage, and the overdischarge voltage indicates a dischargeable lower limit voltage.
During charging, that is, when a charger 200 is connected between the first external terminal 120 and the second external terminal 130, the respective batteries BT1 to BTn are charged. Even during the charging, the battery state monitoring circuit 100 monitors the charged state through detection of the voltages of the respective batteries BT1 to BTn. Upon detecting that the voltage of at least one battery of the respective batteries BT1 to BTn is equal to or more than the overcharge voltage, the battery state monitoring circuit 100 controls the switch circuit 110 to be turned off, and prohibits the charging to the respective batteries BT1 to BTn.
On the other hand, during discharging, that is, when a load 300 is connected between the first external terminal 120 and the second external terminal 130, the respective batteries BT1 to BTn are discharged. Even during the discharging, the battery state monitoring circuit 100 monitors the discharged state through detection of the voltages of the respective batteries BT1 to BTn. Upon detecting that the voltage of at least one battery of the respective batteries BT1 to BTn is lower than the overdischarge voltage, the battery state monitoring circuit 100 controls the switch circuit 110 to be turned off, and prohibits the discharging to the load 300 (for example, refer to the following Patent Document 1). Patent Document 1: JP 2002-320324 A